1. Field of the Invention
The present invention relates to an electronic apparatus and power supply method of supplying electric power to a partner apparatus.
2. Description of the Related Art
By the IEEE1394-1995 standard, electric power can be supplied to an apparatus connected by a 6-pin cable. However, an apparatus on the supply side need not supply power even though a 6-pin cable is used. When electric power is to be supplied, it is defined that a voltage of 8 to 30 V and a maximum of 1.5 A/port can be supplied. An apparatus connected by a 6-pin cable can freely choose whether to operate by electric power supplied from the connected cable or by electric power from its own power source.
As described above, the power supply side can choose whether to supply power according to convenience, and the power consuming side can choose whether to consume supplied power according to convenience. The power capacity of each of the supply side and consuming side is indicated by information contained in a self-ID packet. This self-ID packet contains information indicating the attribute of an apparatus, and is transmitted to a 1394 network by the apparatus when a cable is inserted into a 1394 bus or when electric power is supplied.
A signal line for data transfer and a power line for power supply are integrated into one cable and connected to one connector.
Unfortunately, this power supply technique has the following problem.
An apparatus on the power supply side supplies power without knowing the identity of a partner apparatus on the power consuming side. If this partner apparatus is of bad behavior or has a malicious intent, the apparatus may give damage to a power supply circuit of the apparatus on the supply side.
To avoid this problem, a circuit such as a current limiting circuit or fuse can be inserted. In this case, however, electric power is still supplied to an unidentified partner apparatus. The higher the perfection of the countermeasure against this problem, the higher the cost.